Re: [Plib-users] Help for code that is not documented and is confusing
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Re: [Plib-users] Help for code that is not documented and is confusing
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From: Dimitris M. <dm...@ya...> - 2007-07-24 19:58:39
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Yes you are right, about the division, and the assumptions you made have a =
meaning.=0AThe PointPicker? I don;t have this tutorial!!! Can you send it t=
o me plz?=0AI tried also to inverse the elements of this matrix inv[..], on=
ly those apart from [2]. Because if you touch the [2] dimension=0Athe resul=
t is awful...=0A=0AWhat to say, I am very thankfull for your help, John.=0A=
=0A----- Original Message ----=0AFrom: Fay John F Dr CTR USAF 46 SK <john.f=
ay...@eg...>=0ATo: PLIB Users <pli...@li...>=0A=
Sent: Tuesday, July 24, 2007 10:41:34 PM=0ASubject: Re: [Plib-users] Help f=
or code that is not documented and is confusing=0A=0ADimitris,=0A=0A A f=
ew more answers:=0A=0A The "PointPicker" demo program in PUI has a "=
point and=0Aclick" capability to select an object. You start the program, =
click=0Atwice in the gray input box, and then right-click on one of the squ=
are=0A"points" in the main window. When you first start the program you ha=
ve=0Ato click twice in the input box before trying to select a point, but=
=0Aafter the first time you only need to click once; I do not know why this=
=0Ais. The selected point turns red and its point number appears in the=0A=
input box.=0A=0A In your code snippet, I do not know why the inverse=
=0Amatrix is being used. I think the minus signs are related to the fact=
=0Athat it is an inverse matrix; the red book on page 478 gives the matrix=
=0Ain question. I also don't know whether "hot" is "height of terrain" or=
=0A"height over terrain". In the first case it would be the altitude of=0A=
the terrain above some zero point; in the second case it would be the=0Ahei=
ght of your point over the terrain. I do know that "hgt" is short=0Afor "h=
eight". The "for ( int i" loop is stepping through all the hits=0Areturned=
by the "ssgHOT" call and finding the one with the greatest=0Aheight. Agai=
n, I'm not sure why the code sets " hgt =3D - h->plane[3] /=0Ah->plane[2]" =
since using the homogeneous coordinates (page 476 of the=0Ared book) I woul=
d expect " hgt =3D - h->plane[2] / h->plane[3]".=0A=0AJohn F. Fay=0ATechnic=
al Fellow=0AJacobs Technology TEAS Group=0A850-883-1294 =0A=0A-----Original=
Message-----=0AFrom: pli...@li...=0A[mailto:pl=
ib-...@li...] On Behalf Of Dimitris=0AMexis=0ASen=
t: Monday, July 23, 2007 4:42 PM=0ATo: pli...@li...=0AS=
ubject: [Plib-users] Help for code that is not documented and is=0Aconfusin=
g=0A=0AHello people, I am trying to study plib and do some tricks with it, =
I=0Afound code for doing things. No dicent documentation though. So=0Aevery=
thing I tried I did it blindly....=0ACan some one help me with the code sni=
ppets below ?=0A=0AFIRST :=0A=0A /* Look for the nearest polygon *beneat=
h* my_position */=0A float HOT_TOLERANCE =3D 1.0f;=0A ssgHit *results=
;=0A int num_hits;=0A float hot; /* H.O.T =3D=3D Height Of Terrain *=
/=0A sgVec3 HOTvec;=0A sgMat4 invmat;=0A sgMakeIdentMat4( invmat )=
;=0A invmat[3][0] =3D - my_position[0];=0A invmat[3][1] =3D - my_posi=
tion[1];=0A invmat[3][2] =3D 0.0f;=0A=0A sgSetVec3( HOTvec, 0.0f, 0.0=
f, -my_position[2] + HOT_TOLERANCE=0A);//FIXME I don't know why I use minus=
here!!=0A num_hits =3D ssgHOT( scene, HOTvec, invmat, &results );=0A =
hot =3D DEEPEST_HELL;=0A for ( int i =3D 0; i < num_hits; i++ ) {=0A =
ssgHit *h =3D &results[i];=0A float hgt =3D - h->plane[3] / h->=
plane[2];=0A if ( hgt >=3D hot ) {=0A hot =3D hgt;=0A =
if ( normal !=3D NULL )=0A sgCopyVec3( normal, h->pl=
ane );=0A }=0A }=0A return hot;=0A}=0A=0ABesides the fact that=
I took as "global constant" the code, I didn;t=0Aunderstand why the invers=
e matrix! ?=0AWhat is supposed to do ?=0A=0Alower You see a FIXME, it is mi=
ne, and yes what does this line do ?=0AIf I have a 3000polygon coming again=
st 5000 polygons of another surface,=0Athe for loop, goes all this around t=
o seek the collition?=0AWhat is, really ssgHit, and the division with float=
hgt ?=0A=0ANext I want to ask about the code in PPE about picking...To tel=
l you the=0Atruth I read OpenGL book about glLoadName* but I don't see how =
that=0Awould fit here when I load a model and not drawing vertices....=0AHa=
s anyone tried to draw something in 3D from his mouse click? e.g. the=0Aray=
and try to intercect with the objects in the scenery?=0AOR has anyone achi=
eved to point and click an object ? I haven't seen=0Acode to do that from p=
lib...apart ppe, which ppe neither compiles nor=0Ahas some remarks to under=
stand it's stuff...=0A=0ACrying for help...=0ADimitris=0A=0AThank you=0A=0A=
=0A=0A=0A =0A________________________________________________________=
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